Many video games involve a user controlling an on-screen persona. Examples are a character (e.g., Mario in Super Mario Bros. by NINTENDO), a vehicle (e.g., a ship in Galaga by MIDWAY GAMES Inc.), a realm (e.g., a city such as in SimCity by MAXIS, or a military group (e.g., Terrans in StarCraft by BLIZZARD ENTERTAINMENT). Many of these games provide a way for the persona to obtain a bonus to make the persona more powerful or the game easier to play, e.g., through power ups or virtual items, or by developing certain technologies as part of the gameplay.